1. Field of the Invention
The invention relates to a heat insulation system for surfaces along which a hot gas stream is conducted.
2. Description of the Related Technology
Heat insulation systems may be used in nuclear power station construction for heat protection of the prestressed concrete pressure vessel enclosing the nuclear reactor. Insulation may be used for protecting gas conduits in which the heated gas coming from the nuclear reactor is conducted to the further components of the primary circuit. In the first case, the heat insulation system is attached to a liner of the pressure vessel cavern as the support structure. In the second case the heat insulation system is the pressure jacket of the gas conduits.
The heat insulation system must be designed in such a manner that a failure can be reliably excluded for the entire operating period under the loads acting on the system (essentially its own weight, pretension forces, acoustical and flow-induced vibration excitation and water after an accident).
The functional capability, that is to say the insulating effect of the insulating material can be considered to be ensured if the insulating material does not change its position between the support structure and the cover plates. Cavities formed in the heat insulation system due collapsing or slipping-down of the insulating material must be avoided. This risk exists particularly in vertical areas of the heat insulation system, for example at the vertical walls of a prestressed concrete pressure vessel. In these areas of the building section to be protected, the ceramic fiber material is held in position by vertical forces of friction between the fibers and its boundary walls. The force of friction must be greater than the weight of the fiber mats to avoid a collapsing of the fiber mats between these boundary walls and thus a decrease in their dimensional stability. A restoring force must be present which has still not disappeared even after all possible accidents. This must be obtained at the cost of initially higher compression of the fiber mats since, as is known, the restoring force becomes less with time and due to the effects of temperature and water.
German patent specification No. 29 49 726 shows a heat insulation system intended for a gas duct for connecting the hot gas collection space of a gas-cooled high temperature reactor to a steam generator. The insulating material consists of several layers or plies which are separated from one another by intermediate plates. Lining plates can be provided between the insulating material layers and the intermediate plates. The rectangular cover plates are fixed in position by centrally arranged holding boxes as is usual and are additionally held by bolts provided at the corners of the cover plates. Furthermore, convection barriers are also arranged in the insulating material. The convection barriers are frames which enclose one layer of the insulating material.
A further thermally insulated gas duct is described in German Offenlegungsschrift 29 45 877. Cover plates attached to the support structure cover the insulating material of the hot side. Plies of ceramic fiber mats which are slightly compressed by the cover plates can be used as insulating material. In this case, however, the plies are not separated by intermediate plates. Spacing sleeves are pushed onto the holding bolts of the cover plates in order to render the position of the cover plates independent of the restoring forces of the insulating material.
German Offenlegungsschrift 29 45 921 shows a high permeability thermal insulation for the inside wall of a prestressed concrete pressure vessel. The insulation consists of individual plies of insulating material separated by intermediate plates, cover plates and holding bolts. In this case, a multiplicity of loose steel strips are used as insulating material and a sealing foil which is closely welded together over its entire area is applied to the topmost layer of the intermediate plates.
Patent application Ser. No. P 38 12 572.2, shows a heat insulation system having several plies of slightly compressed ceramic fiber mats. Rectangular cover plates are attached to the hot side of the fiber mats. Intermediate plates are arranged between the plies of the fiber mats. The intermediate plates may hold the fiber mats and seal the insulation. The intermediate plates act to transfer force in vertical areas. A multiplicity of holding bolts are mounted on a support structure situated on the cold side of the fiber mats. The bolts penetrate through holes in the cover plates, the fiber mats and the intermediate plates.
The current invention is an improvement on DE No. 38 12 572. The intermediate plates are constructed as nail plates and have nails on both sides. The nails are supported against the centrally arranged holding bolts in the cover plates. The nails transfer the forces from the fiber mats to the intermediate plates.